1. Field of the Invention
The present invention relates to a rubber hose for transporting a hydrogen fuel used for a fuel-cell powered vehicle. More particularly, the invention is concerned with such a rubber hose used as a conduit or piping for transporting the hydrogen fuel in a fuel-cell powered automotive vehicle as a next-generation vehicle.
2. Discussion of Related Art
In recent years, problems of depletion of the fossil fuel and environmental pollution such as the acid rain, global warming phenomenon, etc., have been getting serious throughout the world. In view of this, a fuel-cell powered vehicle which assures high energy savings and which does not emit harmful exhaust gases has been developed as an alternative for a gasoline or diesel vehicle. As is well known, the fuel-cell powered vehicle is equipped with a fuel cell wherein hydrogen and oxygen (air) electrochemically react with each other, so as to generate electricity with which an electric motor of the vehicle is operated to drive the vehicle.
To the negative electrode of the fuel cell, a hydrogen fuel such as a pure hydrogen gas or hydrogen obtained by reforming a natural gas, methanol, gasoline, etc., is supplied via a piping. As the piping for transporting such a hydrogen fuel, there has been proposed a metal tube formed of a stainless steel, for instance and exhibiting a high degree of hydrogen gas impermeability, by taking into account a fact that the hydrogen is explosive when exposed to a certain environment.
The proposed metal tube, however, has a low degree of flexibility or a high degree of rigidity, undesirably reducing a freedom of piping layout. Since not only dry hydrogen but also wet hydrogen including a steam therein flows through the tube, the metal tube may suffer from corrosion due to the steam.
To overcome the problems described above, there has been a demand for a rubber hose which has high degrees of flexibility and freedom of piping layout and which assures easy installation thereof. While there have been proposed various kinds of rubber hoses such as a refrigerant transporting hose used for an air conditioning system and a gasoline fuel transporting hose, none of the conventionally proposed rubber hoses satisfy, to a sufficient extent, the characteristics required by the hydrogen fuel transporting hose used for the fuel-cell powered vehicle.
The hydrogen fuel transporting hose is generally required to exhibit high degrees of gas impermeability, in other words, hydrogen gas impermeability, for preventing a leakage flow of the hydrogen fuel through the hose, and corrosion resistance to steam, a high degree of insulation performance, in other words, a high electric resistivity, for preventing a leakage flow of the electric current from the fuel cell as the electric generator, and low ion extractability for substantially preventing ions such as metal ions and sulfur ions from being extracted from the rubber hose into the hydrogen fuel flowing therethrough. It has been desired to develop a rubber hose which satisfies those characteristics to a sufficient extent. If the ions such as the metal ions and the sulfur ions were mixed into the hydrogen fuel flowing through the rubber hose, the hydrogen fuel contaminated with the ions would be supplied to the fuel cell, resulting in contamination of the catalyst and the electrolyte of the fuel cell. In this case, the fuel cell suffers from a reduced efficiency of electricity generation, so that the output of the fuel cell is undesirably lowered.
It is therefore an object of the invention to provide a rubber hose for transporting a hydrogen fuel hose used for a fuel-cell powered vehicle, which rubber hose has high degrees of flexibility, freedom of piping layout, and hydrogen fuel impermeability, while exhibiting a high electric resistivity and a low ion extractability for substantially preventing ions such as metal ions and sulfur ions harmful to the fuel cell, from being extracted from the rubber hose into the hydrogen fuel flowing therethrough.
The above object of the present invention may be achieved according to a principle of the invention, which provides a hydrogen fuel transporting hose for a fuel cell powered vehicle having a laminar structure including at least one inner rubber layer, at least one reinforcing layer, and at least one outer rubber layer, which layers are laminated integrally with one another in the order of description in a radially outward direction of the hose, wherein the improvement comprises: each of the at least one inner rubber layer and the at least one outer rubber layer being provided by a vulcanized rubber obtained by vulcanizing a rubber composition including: (A) a rubber material selected from the group consisting of (a1) a halogenated butyl rubber material, (a2) a blend of a halogenated butyl rubber material and a butyl rubber material, and (a3) an ethylene-propylene rubber material, and (B) a filler whose crystal structure is a layer structure, the rubber composition being vulcanized with one of a peroxide vulcanizing agent and a resin vulcanizing agent where the rubber composition includes, as the rubber material, one of (a1) the halogenated butyl rubber material and (a2) the blend of the halogenated butyl rubber material and the butyl rubber material, while the rubber composition being vulcanized with the peroxide vulcanizing agent where the rubber composition includes, as the rubber material, (a3) the ethylene-propylene rubber material.
Unlike the conventional metal tubes and the resin tubes formed of the respective materials having certain degrees of rigidity, the present hydrogen fuel transporting hose formed of the rubber material has high degrees of flexibility and freedom of piping layout, and assures easy installation thereof. Further, the hydrogen fuel transporting hose according to the present invention is formed of a rubber material suitably selected from among a halogenated butyl rubber material, a blend of a halogenated butyl rubber material and a butyl rubber material, and an ethylene-propylene rubber material, which rubber materials exhibit excellent characteristics such as high degrees of gas impermeability, resistances to steam and weather, etc. Each of the inner and outer rubber layers of the laminar structure of the hose is provided by a vulcanized rubber obtained by vulcanizing the selected rubber material with a peroxide vulcanizing agent or a resin vulcanizing agent, so that the present rubber hose exhibits high degrees of impermeability of hydrogen gas and steam which are included in the hydrogen fuel. In the present rubber hose wherein the selected rubber material is vulcanized with the peroxide vulcanizing agent or the resin vulcanizing agent, the ions such as the metal ions and the sulfur ions which may cause an undesirable trouble with the fuel cell are not substantially extracted from the hose into the hydrogen fuel flowing therethrough, unlike in an arrangement wherein the rubber material is vulcanized with a sulfur vulcanizing agent, using a vulcanization accelerator such as a metal oxide and a metal hydroxide.
To the vulcanized rubber which gives each of the inner and outer rubber layers, there is added a filler whose crystal structure is a layer structure, i.e., layered crystal structure. (This filler is hereinafter referred to as xe2x80x9clayered fillerxe2x80x9d). Unlike the conventional rubber hose in which only carbon black is included therein as a filler or a reinforcing agent, the present rubber hose wherein the layered filler is included exhibits a significantly high electric resistivity and low ion extractability for substantially preventing the ions such as the metal ions and sulfur ions possibly causing an undesirable trouble with the fuel cell, from being extracted from the hose into the hydrogen fuel flowing therethrough. While the mechanism of the low ion extractability exhibited by the layered filler is not sufficiently clear, it is speculated that the ions such as the metal ions are held by and between the adjacent layers of the layered filler, so as to prevent extraction of the ions from the vulcanized rubber.
In the hydrogen fuel transporting hose according to the present invention, the fiber reinforcing layer formed by spiraling or braiding and commonly provided in ordinary rubber hoses is provided between the inner and outer rubber layers, so that the present hose can sufficiently withstand the pressure of the hydrogen fuel flowing therethrough.
In one preferred form of the present invention, the vulcanized rubber which gives each of the at least one inner rubber layer and the at least one outer rubber layer has an ion extractability represented by an electric conductivity of not greater than 50 xcexcS/cm at a temperature of 25xc2x0 C. in an extracted solution of the vulcanized rubber, the extracted solution being obtained by immersing, for 168 hours, 50 g of the vulcanized rubber in 250 ml of pure water kept at 100xc2x0 C. The present arrangement provides the hydrogen fuel transporting hose which advantageously attains the object of the invention.
In another preferred of the present invention, the halogenated butyl rubber material is a chlorobutyl rubber material or a bromobutyl rubber material.
In still another preferred form of the present invention, the ethylene-propylene rubber material includes a ternary copolymer of ethylene-propylene-diene, a binary copolymer of ethylene-propylene, and a blend of the ternary copolymer of ethylene-propylene-diene and the binary copolymer of ethylene-propylene.